1. Field of the Invention
This invention relates to a novel acetate tow in a filter rod used to filter smoke of a cigarette, and a method of manufacturing same. More particularly, this invention relates to an acetate tow having a high crimp modulus and having no tendency to get is caught on a feed roller of a filter rod making machine when the machine is operated.
2. Description of the Related Art
It is well known that the purpose of a cigarette filter is to reduce the influence on human health of smoking a cigarette, and that an acetate tow is mainly used as the conventional cigarette filter, i.e., as a filler in a filter rod used to filter the smoke of a cigarette. As is also well known, when the acetate tow is used to filter the smoke of the cigarette, the acetate tow uniformly collects whole components of the smoke but the taste of the filtered smoke remains good. To make the filter rod by using a filter rod making machine, the acetate tow is first bloomed, and the bloomed tow is wrapped in paper to form a filter.
FIG. 2 shows an example of a filter rod making machine 10 currently in wide use for making the filter. In FIG. 2, 1 is an acetate tow fed to the filter rod making machine 10, 2 a pair of pretensioning rollers, 3 a pair of feed rollers, 4 a pair of delivery rollers, 5 a wrapping paper, 6 a rod making device, and 7 a knife. Although only one pair of feed rollers 3 is used in the filter rod making machine illustrated in FIG. 1, two pairs of feed rollers may be used.
The acetate tow 1 is applied with a stretch force of between 1.4 and 2.5, by one or two operations, in an area between the pair of pretensioning rollers 2 and the pairs of feed rollers 3, and then relaxation is allowed in the acetate tow between the pair of feed rollers 3 and the pair of delivery rollers 4, to bloom the acetate tow 1. The high stretching force applied during the tow stretch treatment causes a complete removal of part of the crimps in the acetate tow, and therefore, when the filter rod is formed by wrapping the thus bloomed acetate tow with paper, the pressure drop of the air for the filter rod becomes too low, and further, a filtration efficiency of the smoke becomes too low. To solve the above problem, it has been proposed that a degree of relaxation of the acetate tow 1 be made larger, in such a manner that a large recovery of the crimp of the acetate tow after the stretching treatment is realized, to raise the pressure drop for the filter rod, but in this case, the acetate tow has a tendency to be caught on the feed rollers of the filter rod making machine, and thus production of the filter rod becomes difficult in practice.
Japanese Unexamined Patent Publication (Kokai) No. 56-53233, for example, proposed a method in which the acetate tow is treated, at a position upstream of a stuffing box type crimping apparatus, with steam to make the Young's modulus of the acetate tow higher or to make the number of crimps in the acetate tow larger. In the above method, however, no irregular crimp often generated due to fluctuations of the temperature of the steam, and further, this method has problems such that when the temperature of the steam becomes slightly lower than the predetermined temperature, no improvement of the Young's modulus can be obtained, and when the temperature of the steam becomes slightly higher than the predetermined temperature, the fibers in the acetate tow adhere to each other.